This invention relates to a novel process for preparing a chemically modified bitumen by admixing, at an elevated temperature, a bitumen with a composition prepared by admixing a petroleum fraction with a polymer and free sulfur. The invention is also concerned with the product obtained by the aforesaid process.
The instant process produces modified bitumens possessing a combination of properties which make them useful for use as binders for road top coatings. A binder for road top coatings comprises bitumen--pure or containing polymers--to which is added fluidizing agents such as petroleum fractions or a coal-tar oil having a distillation range generally between 100.degree. and 350.degree. C. The fluidizing agent is necessary to make it possible for the bitumen or the modified bitumen to be used that is, spread when hot, by spreading equipment well known in the public works industry. It is known that the mechanical properties of bituminous binders are improved by the addition of elastomers.
Elastomers used to improve the properties of bitumen compositions include polyisoprene, butyl rubber, polyisobutene, ethylene-vinyl-acetate copolymers, polymethacrylates, polychloroprenes, styrene-butadiene rubber statistical copolymers, styrene-butadiene sequenced copolymers, and the like.
Among these elastomers, disequenced or multisequenced copolymers having a base of styrene and butadiene are known for their effectiveness. They are soluble in the bitumen to which they impart good mechanical properties as well as excellent elasticity.
It is known that the stability of such compositions can be increased and their scope of use enlarged by chemically coupling the bitumen and the polymers.
However, to obtain a homogeneous mixture, when it is possible, by the direct solubilization of the elastomer in the bitumens, the use of very effective mixing and stirring means is required as well as elevated temperatures generally between 180.degree. C. and 200.degree. C.
The direct solubilization requires long periods of time and substantial amounts of energy which have a pronounced impact on the cost of the operation.
The products obtained by the direct solubilization of the elastomers, even if they have acquired good mechanical properties, are characterized by high viscosities that make them difficult to spread by conventional chutes used in the spreading equipment. Further, to use the bitumens containing the directly solubilized elastomers, it is necessary
(a) to modify the spreading equipment by providing the chute, for instance, with a hot oil circulation and therefore it is necessary to use more sophisticated equipment adapted to the new type of product, or PA1 (b) to find the conditions for emulsification of the product and spread it in the form of an aqueous emulsion. The conditions for emulsification may vary from one bitumen-polymer mixture to another and their use is difficult, or PA1 (c) to reduce the viscosity of the product to a convenient viscosity by addition of a solvent. Addition of a solvent, and an added mixing step, requires the difficult control of the supply product and solvent to the mixture. PA1 (1) 75 to 80% by weight of a coal tar oil or petroleum fraction having a boiling range at atmospheric pressure of from 100.degree. C. to 350.degree. C., usually employed for cutting back (fluidizing) bitumens, PA1 (2) 20 to 25% by weight of a styrene-butadiene disequenced or multisequenced copolymer of a molecular weight varying between 30,00 and 300,000 preferably 70,000 to 200,000 and PA1 (3) 0.5 to 1.5% by weight of sulfur used as a reagent and
The object of this invention is to overcome the difficulties and shortcomings of the prior art procedures by providing a process for the preparation of new fluid compositions of bitumens chemically coupled with polymers than can be directly used by conventional spreading means.